CONTRIBUTIONS  FROM  THE  BOTANICAL  DEPARTMENT  OF  THE 
UNIVERSITY  OF  NEBRASKA. 

IfcTETO-     SERIES, 


THE  BOTANY  OF  THE  APPLE  TREE. 


BY  CHARLES  E.  BESSEY,  PH.  D. 

\\ 

ASSISTED   BY   ALBERT   F.    WOODS,    A.    M. 


Extracted  from  the  Annual  Report  of  the  Nebraska  State  Horticultural  Society,  1894.. 


DISTRIBUTED  MARCH  27,   1894. 


LINCOLN,  NEBRASKA. 
U.  S.  A. 


THE  BOTANY  OF  THE  APPLE  TREE. 


BY  CHARLES   E.    BESSEY,  ASSISTED  BY   A.    F.  WOODS. 


The  apple  tree  is  a  near  relative  of  the  roses,  raspberries,  black- 
berries, strawberries,  and  is  somewhat  further  removed  from  the  plums, 
peaches,  cherries,  etc.  It  is  therefore  a  member  of  the  rose  family 
(Rosacece),  and  has  many  characteristics  common  to  the  one  thousand 
related  species. 

The  place  of  this  family  among  the  flowering  plants  of  the  vegetable 
kingdom  has  been  a  matter  of  some  controversy,  but  the  more  rational 
view  is  the  one  which  regards  its  species  as  standing  not  far  from  the 
lower  or  primitive  dicotyledons  (i.  e.,  plants  with  two  seed  leaves),  and 
hence  not  distantly  related  to  the  buttercups,  anemones,  etc.  Indeed 
it  is  not  difficult  to  see  in  the  strawberry,  raspberry,  and  blackberry, 
and  even  in  the  apple  itself,  a  good  many  resemblances  to  buttercups 
and  anemones.  If  the  receptacle  of  a  buttercup  should  become  fleshy 
we  would  have  a  pretty  close  imitation  of  a  strawberry.  If  we  com- 
pare the  species  of  Spiraea  with  some  of  the  members  of  the  butter- 
cup family,  the  resemblance  is  still  more  striking.  It  is  safe  for  us  to 
assume,  therefore,  that  the  family  of  plants  to  which  the  apple  belongs 
is  not  one  of  high  botanical  rank,  however  high  we  may  rank  it  from 
an  economic  standpoint. 

In  the  rose  family  there  are  several  marked  types  of  flowers,  of 
which  the  most  important  are  the  following :  (1.)  With  several,  sepa- 
rate, free  pistils,  as  in  the  strawberry,  blackberry,  raspberry,  Spiraa, 
etc.  (2.)  With  several  pistils  which  are  covered  with  the  adherent 
calyx-tube,  as  in  the  apples,  pears,  quinces,  etc.  (3.)  With  but  one 
free  pistil,  as  in  cherries,  peaches,  plums,  etc. 

The  plants  of  the  second  type  are  sometimes  set  off  in  a  sub-family 
called  the  apple  sub-family  (Pomacece),  and  occasionally  this  has  been 
regarded  as  a  distinct  family  under  the  same  name.  In  the  apple 
sub-family  botanists  have  been  able  to  distinguish  fourteen  different 

(7) 

678005 


O  NEBRASKA   STATE   HORTICULTURAL   SOCIETY. 

genera,  of  which  the  most  important  from  the  horticulturist's  stand- 
point are  the  following:  Cotoneaster,  of  which  one  or  more  species 
are  in  common  cultivation  as  pretty,  thorn-like  trees;  Cydonia,  the 
quinces ;  Pirus,  the  apples ;  Eriobotrya,  the  Japanese  medlars  ;  Amei- 
anchier.  the  service  berries ;  Mespilus,  the  common  medlars;  and  Cra- 
tcegus,  'tlie  hawthbrnes.  In  this  paper  we  are  particularly  concerned 
;^khjthb'getou3  w.hisb  includes  the  apples,  and,  as  will  be  seen  below, 
even  here  we  need  notice  but  a  few  of  the  many  species. 

PIRUS  L. 

Flowers  containing  both  stamens  and  pistils;  calyx  a  five-lobed  cup 
adhering  to  and  enclosing  the  two  to  live  ovaries;  petals  five,  inserted 
on  the  top  of  the  calyx  cup ;  stamens  many  (about  20)  inserted  on 
the  top  of  the  calyx  cup  ;  ovaries  usually  with  two  ovules,  producing 
as  many  seeds ;  fruit,  a  pome,  consisting  of  the  enlarged  and  fleshy 
calyx  cup,  enclosing  the  papery  carpels  (core)  and  brown,  tough- 
coated  seed  ;  leaves  alternate,  deciduous,  simple  or  compound. 

About  fifty  species  of  this  genus  are  now  known,  mostly  natives  of 
the  north  temperate  zone,  a  few  extending  into  the  tropics  upon  high 
mountains.  Seven  or  eight  species  occur  in  North  America. 

The  genus  is  divided  into  six  sub-genera,  namely  : 

1.  The  Apples  (Mains),  with  globose  fruit,  containing  soft  flesh ;  leaves 

simple. 

2.  The  Pears  (Eupirus),  with  pear-shaped  fruit,  containing  granular 

flesh  ;  leaves  simple. 

3.  The  Beam- Trees  (Aria),  with  pear-shaped  or  globose  fruit,  contain- 

ing granular  flesh  ;  leaves  simple. 

4.  The  Choke- Berries  (Aronia),  with  berry-like,  pear-shaped,  or  glo- 

bose fruits,  and  simple  leaves. 

5.  The  Dwarf- Apples  (Micromeles),  with  small  apple-like,  2  to  3  celled 

fruits,  and  simple  leaves. 

6.  The  Mountain    Ashes  (Sorbus),   with  berry-like  mostly  3-celled 

fruits,  and  compound  leaves. 

In  this  paper  the  species  of  the  first  sub-genus  only  will  be  noticed, 
inasmuch  as  they,  alone,  are  properly  entitled  to  the  name  "Apple." 
All  the  species  considered  here  are  of  more  or  less  horticultural  in- 
terest. 


THE  BOTANY  OF  THE  APPLE  TREE. 
THE  APPLE  SPECIES. 

SECTION  1.  Calyx-lobes  persistent  upon  the  ripe  fruit;  styles  5; 
fruits  5-celled. 

A.  Leaves  folded  in  the  bud,  more  or  less  pinnately  lobed;  flowers 

white  or  pink ;  trees  more  or  less  thorny. 

1.  EASTERN  APPLE  (Pirns  coronaria  L.)  Leaves  ovate  to  tri- 

angular-ovate, sharply  cut-serrate,  and  often  3-lobed ;  twigs 
and  leaves  soon  smooth;  flowers  on  smooth  pedicels;  ripe 
fruit  depressed-globose,  yellow-green,  1  to  1 J  inches  in  di- 
ameter. A  shrub  8  to  10  feet,  or  small  tree  20  to  30  feet 
high.  Native  of  North  America,  from  New  York  to  Michi- 
gan, and  south  to  Georgia  and  Alabama,  and  frequently 
planted  for  ornamental  purposes. 

2.  PRAIRIE  APPLE  (Pirus  ioensis  (Wood)  Bailey).     Leaves  el- 

liptic-oblong to  ovate-oblong,  irregularly  and  obtusely 
toothed  ;  twigs  and  under  surface  of  leaves  white-woolly ; 
flowers  on  white- woolly  pedicels;  ripe  fruit  depressed-glo- 
bose, yellow-green,  1  to  2  inches  in  diameter.  A  shrub  or 
tree  like  the  preceding.  Native  of  the  Mississippi  valley. 
This  is  probably  the  parent  form  of  the  "Soulard  Crab/' 
which  Professor  Bailey  has  described  as  P.  soulardi. 

3.  SOUTHERN  APPLE  (Pirus  augustifolia  Ait.).     Leaves  lanceo- 

late-oblong, coarsely  and  bluntly  toothed ;  twigs  and  leaves 
soon  smooth ;  flowers  on  smooth  pedicels ;  ripe  fruit  de- 
pressed-globose, yellow-green,  f  to  1  inch  in  diameter.  A 
shrub  or  tree  like  the  preceding,  native  from  Pennsylvania 
to  Florida,  and  west  to  the  Mississippi  valley,  and  fre- 
quently planted  for  ornamental  purposes. 

It  is  probable  that  the  three  foregoing  species  are  but  geographical 
varieties  of  one  species,  as  they  show  easy  gradations  from  one  to  the 
other.  The  Prairie  apple  appears  to  be  the  most  valuable,  and  as  a 
consequence  it  is  the  most  promising  as  a  stock  for  the  development  of 
cultivated  varieties. 

B.  Leaves  rolled  in  the  bud,  not  lobed. 

(a.)  Fruit  crowned  by  the  calyx  lobes  only  (not  by  a  tube). 

4.  SMOOTH  WILD  APPLE  (Pirus  silvestris  (Mill.)  Koch). 


10  NEBRASKA    STATE    HORTICULTURAL   SOCIETY. 

ovate,  crenate,  when  young  hairy,  when  old  smooth,  or 
nearly  so;  twigs  at  first  sparsely  hairy,  becoming  smooth, 
flower-stalk  and  calyx  mostly  smooth ;  fruit  yellowish  or 
reddish,  f  inch  in  diameter  on  a  stalk  about  as  long,  very 
sour  and  bitter.  A  tree  25  to  30  feet  high,  native  of  cen- 
tral Europe. 

5.  HAIRY  WILD  APPLE  (Pirus  mains  L.).  Leaves  ovate  or  el- 
liptical, crenate,  more  or  less  hairy,  as  are  the  twigs  also; 
flower-stalk  and  calyx  white-woolly;  fruit  longer  than  its 
stalk,  larger  than  the  preceding,  from  sour  to  sweet.  Two 
quite  well  marked  wild  varieties  are  commonly  recognized 
as  follows: 

var.  dasyphylla,  a  tree  of  moderate  size  with  horizontal 
branches,  bearing  large  leaves  (3  to  4  inches  long  and  2  to 
2J  broad).  Native  of  the  Orient. 

var.  pumila,  a  shrub  or  small  tree,  native  of  southeast  Rus- 
sia, the  Caucasus,  Tartary,  etc.  From  this  variety  have 
come  the  dwarf  apples  known  as  Paradise  and  Doucain  ap- 
ples, so  frequently  used  by  propagators  for  dwarfing  the 
larger  cultivated  sorts. 

This  species  with  its  varieties  appears  to  have  given  rise  to  most  of 
the  cultivated  apples  of  the  world.  It  is  doubtful  whether  the  pre- 
ceding species  (P.  silvestris)  should  be  kept  distinct  from  P.  mains. 
They  appear  to  freely  intercross  and  produce  gradations  from  one  type 
to  the  other. 

The  cultivated  varieties,  as  the  Baldwin,  Jonathan,  Ben  Davis, 
Grimes'  Golden,  are  what  the  botanist  calls  "  horticultural  varieties," 
which  differ  from  varieties  in  the  botanical  sense  by  being  less  stable. 
A  botanical  variety  will  reproduce  itself  from  seed,  but  these  "  horti- 
cultural varieties'7  will  not  do  so.  And  yet  the  two  differ  only  in  de- 
gree, not  in  kind.  The  horticultural  variety  is  a  slight  temporary 
variation  which  will  easily  lose  its  identity,  while  the  botanical  vari- 
ety is  the  same  in  kind,  but  with  such  stability  that  it  reproduces  itself 
year  by  year  from  the  seed. 

The  extremely  variable  character  of  this  species  may  be  inferred 
from  the  statement  made  by  Professor  Bailey,  that  the  horticultural 
varieties  undoubtedly  reach  four  or  five  thousand.*  Downing  gives 

*See  the  article  "Apple"  in  the  new  edition  of  Johnson's  Cyclopaedia,  1893,  pp. 
260-261. 


THE  BOTANY  OF  THE  APPLE  TREE.  11 

descriptions  of  1900  varieties,  and  the  American  Poraological  Society's 
list  includes  369. 

(b.)  Fruit  covered  by  a  short  fleshy  calyx  tube,  bearing  the  calyx  lobes. 

6.  CHINESE  APPLE  (Pirus  spectabilis  Aiton).    Leaves  elongated- 

elliptical,  smooth;  flower-stalk  and  calyx-tube  hairy;  fruit 
about  as  long  as  its  stalk  (1  inch),  yellowish.  A  tree  20  to 
25  feet  high,  native  of  China  and  Japan,  often  found  in  cul- 
tivation, with  much  " doubled"  flowers. 

7.  BJNGO   APPLE  (Pirus  ringo    Seibold.).     Leaves  ovate-elon- 

gated, sharp  serrate,  at  first  hairy  below,  but  eventually 
smooth;  flower-stalk  and  calyx  white-woolly;  fruit  wax- 
yellow  with  a  reddish  tinge,  1  to  1J  inches  in  diameter, 
stalk  about  as  long.  A  small  tree  9  to  10  feet  high,  native 
of  Japan.  Occasionally  cultivated  for  ornamental  purposes. 

8.  LARGE  SIBERIAN  APPLE  (Pirus  prunifolia  Willd.).     Leaves 

ovate,  elongated  or  elliptical,  smooth  below,  on  long  petioles ; 
flower-stalk  and  calyx  hairy  or  smooth;  fruit  wax-yellow, 
to  red  and  even  black,  1  to  1J  inches  or  more  in  diameter, 
stalk  about  as  long  or  longer.  A  tree  25  to  30  feet  high, 
native  of  northern  China,  Tartary,  and  southern  Siberia. 
This  is  the  parent  form  of  the  larger  cultivated  crab  apple, 
such  as  the  Transcendent,  Hyslop,  etc. 

SECTION  2.  Calys  lobes  falling  off  after  blossoming;  styles  3  to  5; 
fruits  3  to  5  celled. 

A.  Leaves  rolled  in  the  bud. 

9.  SMALL  SIBERIAN  APPLE  (Pirus  baccata  L.).     Leaves  elon- 

gated-ovate, smooth,  as  are  the  twigs  also;  flower-stalk 
and  calyx  smooth ;  fruit  small,  J  to  }  inch,  yellow  or  red, 
on  a  much  longer  slender  stalk  (1  to  1 J  inches).  A  tree  25 
to  30  feet  high,  native  of  the  Himalayas,  Amur,  China,  and 
Siberia.  This  is  the  parent  form  of  the  smaller  cultivated 
crab  apples,  as  the  Red  Siberian  Crab,  etc.* 

*  Since  the  preparation  of  this  paper  I  have  seen  Dr.  Alexandra  Batalin's  paper, 
"Notse  de  Plantis  Asiaticis,"  in  Ada  Horti  Petropolilani,  Vol.  XIII  (1893),  pp.  91 
to  106,  in  which  he  describes  another  apple  from  the  province  of  Kansa  in  western 
China,  which  is  apparently  allied  to  Pirus  baccata,  and  which  he  names  P.  transi- 
toria.  It  is  a  tree  abont  20  feet  in  height,  with  long-petio led,  trisected,  or  tripartite 
densely  pubescent  leaves,  and  a  small  globose  fruit,  about  £  inch  in  diameter.  It 
should  be  investigated  by  our  horticulturists,  as  a  possible  stock  for  top  grafting. 


12 


NEBRASKA   STATE    HORTICULTURAL   SOCIETY. 


B.  Leaves  folded  in  the  bud. 

10.  TORINGO  APPLE  (Pirus  toringo  Koch).     Leaves  small,  ovate 

or  elongated,  3  to  5  lobed;  flower-stalk  and  calyx  spar- 
ingly hairy,  or  smooth  ;  fruit  small  spherical,  J  inch  in 
diameter,  on  a  long  stalk.  A  small  tree  12  feet  high,  na- 
tive of  Japan,  occasionally  planted  for  ornamental  pur- 
poses. 

11.  OREGON  APPLE  (Pirus  rivularis  Dougl.).     Leaves  ovate- 

lanceolate,  smooth  and  firm,  dark  green,  serrate;  flower- 
stalk  and  calyx  somewhat  hairy,  or  smooth;  fruit  on  long 
stalks  obovate  oblong,  J  to  f  inch  long,  from  yellowish- 
green  to  yellow  and  even  red,  flavor  "a  pleasant  sub-acid." 
A  tree  30  to  40  feet  high,  native  of  the  Pacific  coast  01 
North  America  from  California  to  Alaska.  This  species 
should  receive  the  attention  of  the  scientific  horticulturists 
of  the  western  coast  states. 

REMARKS   ON   THE   FOREGOING  SPECIES. 

From  this  view  of  the  species  noticed  above  it  is  seen  that  three  are 
natives  of  eastern  North  America,  one  of  western  North  America, 
two  of  Europe,  three  of  China  and  Japan,  and  two  of  the  Siberian 
region.  Of  these  we  have  brought  into  cultivation  for  their  fruits 
one  species  from  eastern  North  America,  one  or  two  from  Europe,  and 
two  from  the  Siberian  region.  The  species  from  China  and  Japan  are 
ornamental,  as  are  also  those  from  North  America.  These  facts  may 
be  shown  more  clearly  by  the  following  table: 


No. 

Name. 

Nativity. 

Cultivated  or  Not. 

1 

Eastern  apple  

Eastern     North 

America  

For  ornament  only. 

9 

Prairie  apple  

Mississippi  Valley 

For  ornament  and  for  fruit. 

3 

Southern  apple  

Southern  states  ... 

For  ornament  only. 

11 

Oregon  apple  

Pacific    coast    of 

J 

Smooth  W^ld  apple 

North  America- 
Europe 

Sparingly  cultivated  for  ornament. 
Probably  cultivated  for  its  fruit. 

5 

Hairy  ^^ild  apple 

Europe 

Cultivated  for  its  fruit. 

fi 

Chinese  apple 

China  and.  Japan 

Cultivated  for  ornament. 

7 

Ringo  apple 

Japan   .          . 

Cultivated  for  ornament. 

10 

Toringo  apple  

Japan  .           .. 

Cultivated  for  ornament. 

8 

Large  Siberian  apple 

Siberia,  Tartary, 
and  China  

Cultivated  for  its  fruit. 

9 

Small  Siberian  apple 

Siberia,      Amur, 
and  China  .  . 

Cultivated  for  its  fruit. 

THE  BOTANY  OF  THE  APPLE  TREE.  13 

THE  TREE  IN  HEALTH. 

The  healthy  apple  tree  derives  a  portion  of  its  food  from  the  soil 
into  which  its  roots  penetrate.  This  food  consists  of  various  sub- 
stances, the  chief  of  which  is  water,  in  which  all  the  other  food  sub- 
stances are  dissolved.  No  substance  is  taken  up  by  the  roots  in  a 
solid  state,  but  in  every  case  the  food  from  the  soil  must  be  dissolved 
in  water  before  it  can  be  absorbed.  The  particular  organs  of  absorp- 
tion are  the  younger  portions  of  the  small  roots,  and  the  minute  hairs 
which  clothe  the  surface  of  new  roots.  The  statement  still  to  be  seen 
in  popular  books,  and  often  repeated  in  some  journals,  that  the  watery 
matters  in  the  soil  are  taken  up  by  "spongioles"  on  the  tips  of  the 
roots  is  a  gross  error.  There  is  no  such  thing  as  a  "spongiole"  at 
the  end  of  any  of  the  roots,  and  it  is  strange  how  so  palpable  an  error 
should  have  been  continued  for  so  long.  The  very  tip  of  the  root 
where  the  "  spongiole  "  was  supposed  to  be  takes  no  active  part  in  the 
absorption  of  food  matters  from  the  soil. 

In  addition  to  water  itself,  the  other  food-matters,  are  (1)  some  nitro- 
genous substances,  (2)  salts  of  lime,  (3)  salts  of  potash,  (4)  salts  of 
phosphorus,  (5)  salts  of  iron,  and  probably  small  quantities  of  a  few 
others.  The  nitrogenous  substance  may  be  a  salt  of  ammonia,  such  as 
would  be  supplied  by  barn-yard  manure,  or  it  may  be  a  nitrate  such 
as  manure  supplies,  as  well  as  many  of  the  commercial  fertilizers. 
Most  soils  contain  enough  of  the  salts  of  lime  and  potash  for  the 
supply  of  the  tree,  but  they  do  not  all  contain  enough  of  the  phos- 
phorus and  iron,  and  these  may  profitably  be  added  to  the  soils  in 
small  quantities.  Decaying  bones  and  rusty  scraps  of  iron  in  the  soil 
will  supply  all  that  the  tr£e  requires. 

The  supply  of  food  which  the  tree  derives  from  the  air  is  in  certain 
respects  more  important  than  that  which  it  obtains  from  the  soil. 
The  green  leaves  absorb  carbon  dioxide  (commonly  called  carbonic 
acid  gas)  from  the  air,  in  which  it  exists  in  minute  quantities.  Car- 
bon dioxide  is  a  heavy,  poisonous  gas,  composed  of  carbon  and  oxygen. 
It  is  produced  in  the  burning  of  wood,  oil,  illuminating  gas,  and  in  fact 
it  is  one  of  the  products  of  the  burning  of  nearly  all  common  substances. 
This  gas  is  absorbed  by  the  green  leaves,  entering  through  the  little 
pores  found  in  great  numbers  on  the  under  surface.  It  may  not  be 
generally  known  that  upon  every  leaf  there  are  immense  numbers  of 
mouth-like  pores,  which  open  and  close  according  as  the  conditions 


14  NEBRASKA   STATE    HORTICULTURAL   SOCIETY. 

are  favorable  or  not.     Upon  a  fair-sized  apple  leaf,  there  are  no  less 

than  from  350,000  to  400,000 
of  these  pores,  and  in  some 
cases  they  run  much  above 
these  almost  incredible  figures. 
In  some  plants,  as  cottonwoods, 
sunflowers,  cabbages,  etc.,  they 
occur  on  both  sides  of  the  leaf, 
but  in  the  apple  they  are  con- 
fined to  the  under  side.  A  tree 
is  thus  a  thing  with  a  myriad 
of  mouths,  through  which  it 

breathes  in  the  carbon  dioxide 
FIG.  1.— A  small  portion  of  the  lower  skin  of 

an  apple  leaf,  showing  the  breathing  pores,    as  one  OI  the   most  important 
magnified  725  times.  of  its  foodg>      It  also   takes  in 

through  its  leaf-mouths  another  gas,  some  of  which  eventually  becomes 
a  part  of  the  plant  body,  and  hence  it  must  be  called  a  food  matter. 
This  gas  is  oxygen,  the  same  gas  which  we  take  into  our  lungs  with 
every  breath  we  inhale. 

The  carbon  dioxide  and  a  little  of  the  water  are  broken  up  in  the 
green  cells  of  the  leaves,  and  from  the  resultant  fragments  starch  is 
made.  The  latter  constitutes  a  more  important  secondary  food  of 
plants,  inasmuch  as  it  contains  almost  exactly  the  same  substances  as 
those  which  constitute  the  bulk  of  the  solid  part  of  the  tree.  Although 
starch  is  made  in  the  green  leaves,  it  may  find  its  way  to  all  parts  of 
the  tree,  even  to  the  remote  roots  away  down  under  ground,  and  every- 
where, sooner  or  later,  it  is  used  by  the  plant  in  the  building  up  of 
its  substance.  At  the  same  time  the  other  food  substances  taken  in  by 
the  roots  are  used  by  the  different  parts  of  the  plant  as  needed.  The 
idea  sometimes  advanced  that  all  food  matters  taken  in  by  the  roots 
must  go  to  the  leaf  in  order  to  be  "  elaborated,"  is  quite  erroneous. 
These  substances  are  used  whenever  they  are  needed,  whether  in  the 
roots  themselves,  or  in  the  twigs,  or  even  the  leaves  of  the  tree  top. 

There  is  one  thing  which  must  be  discussed  at  this  point,  although 
it  is  only  indirectly  connected  with  the  question  of  the  food  of  the 
tree.  I  refer  to  the  loss  of  water  from  the  aerial  parts  of  the  tree, 
and  particularly  irom  the  leaves.  It  can  easily  be  shown  that  the 
inside  of  a  leaf  is  much  more  moist  than  the  air  which  surrounds  it; 


THE    BOTANY   OF   THE    APPLE   TREE.  15 

there  is,  therefore,  a  constant  tendency  of  the  water  to  pass  out  into 
the  air,  and  this  would  take  place  with  great  rapidity  if  it  were  not  for 
the  impenetrable  skin  which  covers  both  surfaces.  This  skin  keeps 
in  the  moisture  of  the  leaves  just  as  the  oiled  paper,  which  florists  use 
so  much,  keeps  in  the  moisture  of  the  flowers.  But,  as  stated  above, 
there  are  breathing  pores  (or  mouths)  in  the  skin  of  the  under  side  of 
the  leaf,  and  when  the  plant  opens  these  for  taking  in  or  giving  off 
gases,  some  moisture  escapes.  When  we  remember  how  many  of  these 
openings  there  are  in  a  leaf  we  can  readily  understand  how  easily  the 
moisture  can  evaporate  when  they  are  open. 

Now  this  loss  of  water  must  be  made  good  or  the  tree  will  perish. 
When  a  leaf  loses  water  its  cells  take  moisture  from  the  twigs;  these 
in  turn  take  from  the  branches,  and  these  again  from  the  trunk,  and 
so  on  to  the  youngest  roots  which  get  their  supply  of  water  from  the 
soil.  There  is  thus  a  movement  of  the  water  toward  the  point  where 
the  loss  occurs,  and  this  movement  is  more  or  less  rapid  as  the  loss  by 
the  leaves  is  more  or  less.  In  damp  weather  there  is  little  or  no  loss 
of  water  from  the  leaves,  and  as  a  consequence  there  is  little  movement 
of  water  in  the  tree.  In  the  winter,  also,  there  is  little  movement  of 
the  water,  since  evaporation  is  reduced  to  little  or  nothing. 

From  what  has  been  said  it  may  easily  be  made  out  that  the  tree 
has  more  water  in  it  in  the  winter,  when  it  loses  little,  if  any,  by  evap- 
oration, than  in  the  summer,  when  its  supply  of  water  is  constantly  be- 
ing reduced  by  the  loss  from  the  leaves,  and  careful  experiments  show 
that  this  is  actually  the  case.  There  is  more  water  in  a  given  bulk  of 
the  tree  trunk,  or  in  the  branches  and  twigs,  in  January  and  February 
than  in  June  and  July. 

A  word  should  be  said  here  about  the  word  "sap"  as  applied  to  the 
watery  part  of  the  apple  tree.  It  is  simply  the  water  in  the  tree  in 
which  various  substances  are  dissolved.  Sap  is  not  a  living  fluid;  it 
is  not  a  kind  of  vegetable  blood.  It  is  more  like  the  watery  mixture 
to  be  found  in  the  alimentary  canal  of  animals  than  like  their  blood, 
and  yet  this  is  not  a  good  comparison  to  make,  as  it  is  likely  to  lead 
to  false  conclusions.  Moreover,  the  sap  is  not  a  circulating  fluid.  It 
does  not  pass  up  and  down  in  currents  like  the  blood  currents  of  ani- 
mals, and  last,  but  not  least,  it  does  not  go  down  into  the  roots  in  the 
fall  and  come  up  in  the  spring. 

The  growth  of  the  tree  which  is  the  most  obvious  to  the  horticult- 


16 


.NP^BRASKA    STATE    HORTICULTURAL   SOCIETY. 


urist  is  that  which  annually  proceeds  from  the  bud.  Now  a  bud  is 
the  stunted,  inactive  end  of  a  shoot,  and  growth  in  the  spring  is 
simply  the  resumption  of  activity.  Even  the  so-called  lateral  buds 
are  in  reality  the  ends  of  very  short  lateral  shoots.  When  the  growth 
of  the  previous  year  is  checked,  at  the  time  that  the  bud  forms  there 
is  a  considerable  deposit  of  food  matter,  generally  starch,  in  the  bud 
itself,  or  near  it.  On  the  advent  of  warm  weather  the  starch  be- 
comes changed  to  sugar  and  is  dissolved  in  the  water  of  the  tree  when 
it  is  ready  for  use  by  the  buds.  Each  bud,  as  it  becomes  sufficiently 
warmed,  absorbs  the  sugary  food  and  growth  at  once  is  resumed ;  the 
stem  elongates,  thus  separating  the  bud  scales  and  bringing  out  the 
young  inner  leaves.  At  the  apex  of  the  stem  new  stem  and  leaves 
are  constantly  produced,  while  below  these  are  as  constantly  developing 
into  their  full  grown  adult  form.  For  a  time  the  growth  at  the  apex 
of  the  stem  excels  that  of  the  rest  of  the  shoot,  but  after  a  time  the 
apical  growth  diminishes,  and,  as  a  consequence,  the  young  leaves  be- 
come bunched  at  the  end  of  the  shoot  in  the  form  of  a  bud.  The 
growth  of  a  stem  in  length  is  thus  an  intermittent  one,  and  the  bud 
is  simply  the  quiescent  winter  condition  of  its  apex. 

The  leaf  of  the  apple  tree  needs  no  description  as  to  its  external 
anatomy,  as  this  is  well  known.  Internally,  however,  its  structure  is 
not  so  generally  known.  It  is  composed  of  very  small  green  cells, 
surrounded  by  a  skin-layer  of  colorless  cells,  and  penetrated  by  a  sup- 
porting framework  of  branching  ribs.  The  green  cells  next  to  the 

upper  skin  are  elongated  and  closely 
packed  side  by  side,  with  one  end 
touching  the  skin.  These  are  the 
so-called  "palisade"  cells  of  the  leaf. 
In  well  grown  leaves  there  are  two 
or  even  three  layers  of  palisade  cells. 
Below  these  the  cells  are  very  loosely 
arranged,  as  is  well  shown  in  Fig. 
2.  Between  all  these  internal  cells 
there  are  free  spaces  which  are  occu- 
pied with  air  and  other  gases  which 
entered  through  the  breathing  pores 

FIG.  2. -Cross  section  of  an  apple  leaf,  mentioned    above,    and    shown    in 
magnified  200  times.  Fig.  1. 


THE  BOTANY  OF  THE  APPLE  TREE.  17 

It  may  serve  to  show  the  complexity  of  the  apparently  simple  ap- 
ple leaf  to  state  that  in  a  smallish  leaf  a  little  more  than  two  and  a 
half  inches  long  there  are  fully  fifty  millions  of  cells,  of  which  no  less 
than  eight  millions  constitute  the  skin  of  the  two  surfaces.  In  the  skin 
of  the  lower  surface  there  are  from  350,000  to  400,000  openings,  the 
breathing  pores. 

The  growth  of  trunk  arid  branches  in  thickness  takes  place  in  this 
wise:  During  the  latter  part  of  spring  and  early  summer  there  is  a 
great  growth  of  soft  cells  between  the  wood  and  the  bark,  and  imme- 
diately the  outermost  cells  begin  changing  to  bark  and  the  innermost 
ones  to  wood.  This  continues  until  there  is  left  but  a  thin  layer  of 
the  soft  cells.  The  next  year  this  thin  layer  grows  rapidly  and  forms 
a  new  mass  of  soft  cells,  which  in  turn  develop  into  bark  and  wood, 
and  so  on.  Usually  there  is  but  one  great  growth  of  these  cells  in 
each  year,  but  in  some  seasons  there  are  two  growths,  so  that  while 
there  is  commonly  but  one  ring  of  wood  formed  each  year,  now  and 
then  there  may  be  two. 

In  this  connection  it  may  be  well  to  state  that  after  a  stern  is  ripened 
it  does  not  elongate.  All  stories  about  the  elongation  of  tree  trunks 
are  founded  upon  erroneous  observations,  or  are  willful  falsehoods. 

The  growth  of  roots  is,  in  nearly  all  respects,  similar  to  that  of  the 
twigs  and  branches.  Here,  however,  there  are  no  buds.  The  end 
of  the  root  is,  however,  much  like  the  end  of  the  stem  inside  of  the  bud. 
If  we  should  compare  the  tip  of  the  stem  in  the  bud  with  the  tip  of 
the  root,  the  difference  would  not  be  very  great.  Then,  too,  in  the 
root,  as  in  the  stem,  the  elongation  ceases  as  soon  as  it  has  become  hard 
and  firm.  An  old  root  never  elongates  its  body.  The  growth  in 
thickness  of  roots  is  precisely  like  that  of  the  trunk  and  branches, 
and  there  are,  consequently,  similar  annual  rings  of  wood. 

With  all  this  growth  year  by  year  there  is  a  constant  death  of  tis- 
sues, which  follows  hard  upon  it.  The  layer  of  new  wood  is  but 
feebly  alive  by  the  end  of  the  season  of  growth,  and  the  new  bark  is 
little,  if  any,  better.  The  thin  layer  of  soft  cells  between  wood  and 
bark,  that  remnant  of  the  previous  year's  active  cells,  the  cambium  of 
the  botanists,  is  all  that  retains  much  life.  The  pith  and  the  medul- 
lary rays  are  but  passive  storehouses  at  the  end  of  the  first  year's 
growth  of  a  twig,  and  after  that  they  are  dead.  In  the  buds  the 
outer  leaves  ("scales")  soon  die,  leaving  the  tiny  central  stem,  and  the 

2 


18 


NEBRASKA   STATE   HORTICULTURAL   SOCIETY. 


inner  leaves  which  alone  are  alive.  In  the  roots  the  tip  retains  its 
vitality,  but  in  the  older  portions  there  is  left  but  the  thin  cambium 
between  the  feebly  active  layers  of  wood  and  bark. 

The  apple  flower  is  too  well  known  to  require  a  full  description,  but 
the  following  summary  may  be  useful : 

There  are  in  the  first  place  five  green  leaves  (sepals*)  grown  to- 
gether at  the  base  of  the  flower,  and  constituting  the  calyx. f  On  the 
top  of  the  calyx  are  the  five  white  or  pinkish  petals,J  collectively 
called  the  corolla. §  Next  there  are  twenty  or  more  thread-like  or- 
gans each  with  a  yellowish  head;  these  are  the  stamens, ||  and  their 
heads  contain  a  yellow  powder,  the  pollen. Tf  There  are  five  seed-pods 


FIG.  3.— Flowers  of  the  apple.     A,  fully  open;  B,  cut  vertically;  C,  the  calyx; 
P,  petals;  S,  stamens;  P,  stigmas  at  the  top  of  the  pistils. 

(pistils  **),  but  their  bases  are  covered  by  the  calyx-tube,  leaving  only 
their  elongated  hairy  styles,  each  capped  with  its  flattish  stigma  (as 
shown  in  Fig.  3  at  P).  In  the  lower  portion  of  each  pistil  there  are 
usually  two  young  seeds  (ovules). 

In  order  that  the  fruit  and  seeds  may  develop  it  is  necessary  that 
the  ovules  should  be  fertilized.  This  is  done  by  the  pollen  when  it 
is  placed  'upon  the  stigma  of  the  seed-pod,  where  it  grows  down  the 
style  to  the  ovule.  The  result  of  fertilization  is  the  formation  of 
seeds,  and  the  development  of  much  fleshy  tissue  in  the  calyx-tube 

*  Pronounced  sep'-als. 
t  Pronounced  ca/-lyx. 
J  Pronounced  pet'-als. 
\  Pronounced  co-rolMa. 
(I  Pronounced  ata'-mens. 
f  Pronounced  pol'-len. 
**  Pronounced  pis'-tils. 


THE    BOTANY   OF   THE    APPLE   TREE.  19 

surrounding  the  seed-pods.  Unless  there  is  fertilization,  therefore, 
there  will  be  no  apples.  Now,  while  every  apple  flower  has  pollen  in 
its  stamens,  it  is  a  well  known  fact  that  the  fertilization  is  usually  ef- 
fected by  pollen  from  another  flower.  This  is  due  to  the  fact  that 
when  the  flower  first  opens,  its  stamens  are  not  quite  mature,  while  the 
stigmas  are  ready  to  receive  pollen.  It  thus  happens  that  before  the 
stamens  of  any  flower  are  ready  to  supply  pollen  to  the  stigmas,  the 
latter  have  received  all  they  need  from  other  flowers.  This  is  effected 
by  bees  of  various  kinds  which  search  the  flowers  for  honey,  their 
bodies  in  the  meantime  becoming  covered  with  pollen  which  they  leave 
upon  the  protruding  stigmas  of  the  successively  visited  flowers.  It  is 
probable  that  self-fertilization  may  take  place,  in  the  absence  of  in- 
sects; in  fact  Mtiller  makes  the  positive  statement  that  such  is  the 
case.*  but  this  must  occur  under  ordinary  circumstances  with  compar- 
ative infrequency,  since  bees  are  very  common,  and  at  the  time  of  ap- 
ple-blossoming are  eager  to  visit  every  honey-bearing  flower. 

It  may  occur,  however,  that  heavy  rains  and  violent  storms  may 
wash  away  the  pollen  before  the  bees  have  carried  it  from  flower  to 
flower.  This  I  have  known  to  occur  more  than  once,  and  as  a  conse- 
quence the  crop  was  very  light.  I  have  no  doubt  that  even  in  such 
seasons  many  more  flowers  would  be  fertilized  if  every  orchard  con- 
tained a  few  strong  swarms  of  bees. 

The  fruit  of  the  apple  consists,  as  has  been  already  said,  of  the 
thickened  and  fleshy  calyx-tube  which  surrounds  and  encloses  the  five 
seed-pods.  At  the  top  of  the  apple  are  to  be  found  the  remains  of  the 
calyx-tips,  hence  this  is  called  the  calyx-end  of  the  apple,  or  in  horti- 
cultural works  it  is  commonly  spoken  of  simply  as  "the  calyx,"  and 
the  depression  in  which  it  is,  as  the  "  basin." 

At  the  opposite  end  is  the  stalk  of  the  apple,  originally  the  flower- 
stalk,  now  deeply  sunken  by  the  downward  growth  of  the  thick  calyx- 
tube.  The  horticulturist  speaks  of  the  depression  at  the  stalk  end  of 
the  apple  as  the  "cavity." 

In  a  longitudinal  section  one  may  see  lines  extending  through  the 
flesh  from  the  cavity  to  the  basin  (Fig.  4,  A,  W  B) ;  these  are  very 
small  threads  of  woody  matter,  and  may  be  designated  as  the  woody 
bundles  :  they  are  in  fact  the  remnants  of  the  framework  of  the  calyx, 

*The  Fertilization  of  Flowers,  by  Prof.  Hermann  Mueller,  English  edition,  page 
238. 


20  NEBRASKA    STATE    HORTICULTURAL   SOCIETY. 

and  correspond  to  the  ribs  and  "veins"  of  ordinary  leaves.  In  a 
cross  section  of  the  apple  they  show  as  little  dots  or  points  (Fig.  4,  B, 
W  B). 

C 


FIG.  4. — A,  longitudinal,  B,  cross  section  of  an  apple;  C, 
the  calyx-tips  (or  "calyx  ")  in  the  "basin";  S,  the  stalk, 
in  the  "cavity";  S  P,  the  five  seed-pods,  or  "core";  W  B, 
the  woody  bundles  of  the  calyx-tube. 

Normally  there  should  be  two  seeds  in  each  seed-pod,  thus  mak- 
ing ten  seeds  for  the  whole  core ;  but  very  commonly  only  one  devel- 
ops in  each  pod,  and  sometimes  both  are  aborted.  On  the  other 
hand,  in  some  varieties,  more  than  two  seeds  form  in  each  pod.  In  a 
general  way  we  may  say  that  it  is  better  for  the  fruit  to  have  few  seeds 
than  many,  as  it  requires  much  food  to  perfect  seeds,  which  otherwise 
might  be  utilized  in  the  fruit  itself. 

THE  TREE  DISEASED. 

The  apple  tree,  in  common  with  all  other  living  things,  is  subject  to 
various  diseases.  Without  attempting  to  enumerate  all  the  diseases 
to  which  it  is  subject  in  different  parts  of  the  world,  the  following 
summary  statement  it  is  hoped  will  be  helpful  to  a  better  understand- 
ing of  its  pathology :  * 

There  are  four  general  causes  of  pathological  conditions  in  plants, 
all  of  which  are  factors  in  the  pathology  of  the  apple  tree. 

I.  UNFAVORABLE  HABITAT. — This  includes  not  only  such  matters 
as  height  above  the  level  of  the  sea,  forest  or  plain  conditions,  etc., 
which  may  have  much  more  influence  than  we  suppose,  but,  also,  the 

*For  a  fuller  discussion  of  the  subject  of  plant  diseases  see  the  article  "Patho- 
logy" (Vegetable),  in  the  new  edition  of  Johnson's  Cyclopedia,  vol.  VI,  from 
which  much  of  what  is  here  given  is  derived. 


THE  BOTANY  OF  THE  APPLE  TREE.  21 

particular  conditions  of  the  soil.  A  soil  may  be  wanting  in  certain 
substances  necessary  for  the  food  of  the  tree:  the  result  will  be  the 
starvation  of  the  tree.  But  a  soil  may  be  fertile  and  still  not  supply 
enough  food.  If  so  hard  that  the  roots  cannot  penetrate  it,  the  tree 
is  starved  as  certainly  as  in  a  barren  soil.  Or  if  the  soil  is  too  dry 
starvation  will  result,  here  intensified  by  the  lack  of  water,  the  most 
important  of  the  food  substances.  But  on  the  other  hand,  in  a 
soil  which  is  too  wet  the  tree  is  starved  again,  because  its  roots  are  in- 
jured by  submersion,  while  the  coldness  of  such  a  soil  also  acts  dele- 
teriously,  both  resulting  in  an  under  supply  of  food.  The  presence  of 
excessive  amounts  of  potash  (and  some  other  salts)  in  the  soil  may  de- 
stroy the  young  roots,  resulting  again  in  starvation. 

II.  UNFAVORABLE  ATMOSPHERIC  CONDITIONS. — When  the  air  is 
very  dry  the  loss  of  water  from  the  leaves  is  excessive  and  may  exceed 
the  supply  obtained  by  the  roots  from  the  soil.  Upon  the  plains  the 
prolonged  periods  of  high  dry  winds  are  peculiarly  trying  to  all  vege- 
tation, and  especially  so  to  such  trees  as  the  apple,  which  has  not  only 
to  meet  the  water-loss  from  its  leaves,  but  also  that  from  its  flowers, 
and  afterwards  from  its  crop  of  fruits  which  remain  on  the  trees  during 
the  summer.  No  doubt  our  trees  are  much  more  enfeebled  from  this 
oause  than  we  are  wont  to  believe.  We  know  that  a  greenhouse  plant 
which  is  kept  for  a  long  time  in  a  semi-wilted  condition  is  eventually 
much  injured,  and  there  can  be  no  doubt  that  the  same  is  true  of  ap- 
ple trees. 

It  is  possible  that  occasionally  the  temperature  of  some  parts  of  the 
tree  may  rise  too  high,  but  upon  this  point  we  still  lack  sufficient  data. 
I  have  no  doubt,  however,  that  in  hot  summer  days  the  exposed  trunks 
reach  a  dangerously  high  temperature. 

The  reverse  condition  of  extremely  low  temperature,  which  is 
reached  in  many  winters,  is  equally  dangerous.  A  healthy  apple  tree 
will  endure  20  or  more  degrees  below  zero  of  Fahrenheit,  and  some 
varieties  will  survive  40  or  even  50  degrees  below  zero.  Yet  the  ex- 
perience of  many  Iowa  apple  growers  twelve  or  fourteen  years  ago, 
who  lost  in  one  disastrous  winter  all.  the  trees  they  had  successfully 
grown  for  twenty  years,  must  be  a  warning  to  us. 

A  quick  alternation  between  a  low  and  a  high  temperature  is  usu- 
ally fatal  to  parts  of  living  plants.  This  is  probably  the  cause  of 
"  sun  scald.'7  When  the  frozen  tree  is  suddenly  thawed  out  by  the 


22  NEBRASKA   STATE   HORTICULTURAL   SOCIETY, 

i 

bright  winter's  sunshine  upon  the  trunk,  to  be  as  suddenly  frozen 
again  at  night,  the  result  is  usually  fatal  to  the  cells  of  the  cambium 
cells  and  those  of  the  young  wood  and  bark. 

III.  MECHANICAL  INJURIES. — Aside  from  wounds    by    natural 
causes,  as  the  breaking  of  branches  and  leaves,  injuries  by  hail,  wind, 
and  lightning,  many  wounds  are  made  by  man  himself,  as  in  pruning, 
pinching  back,  grafting,  budding,  etc.     All  these  wounds,  whether 
made  purposely  or  not,  afford  ready  means  for  the  access  of  bacteria 
and  fungi,  resulting  in  more  or  less  extended  decay  of  the  tissues. 
Even  when  a  wound  is  covered  by  the  growth  of  living  tissues  over 
it,  decay  usually  continues,  extending  deeper  and  deeper  until  it  be- 
comes widespread.     There  can  be  no  question  that  every  wound  is  a 
serious  menace  to  the  life  of  the  tree. 

Under  this  head  must  be  placed  all  the  injuries  by  insects.  These 
affect  all  parts  of  the  tree,  the  roots,  trunk,  branches,  twigs,  flowers, 
and  fruit,  In  many  cases  the  injury  is  one  of  simple  cutting,  as  in 
the  removal  of  parts  of  the  leaves,  the  boring  of  the  stems,  etc.,  but 
if  the  loss  of  leaves  is  excessive  the  tree  may  perish  through  starva- 
tion, and  the  burrows  in  the  stems  may  afford  means  for  the  entrance 
of  bacteria  and  fungi.  Sucking  insects  by  the  withdrawal  of  water 
and  other  food  matters  in  so  far  decrease  the  nutrition  of  the  plant. 
Some  insects,  in  addition,  inject  a  poisonous  or  irritating  fluid  into  the 
wood,  killing  the  tissues  or  setting  up  abnormal  growths,  resulting  in 
the  production  of  galls  and  other  malformations. 

IV.  PARASITISM. — One  of  the  most  fruitful  sources  of  diseased 
conditions  in  the  apple  tree  is  the  presence  of  parasitic  vegetable  or- 
ganisms in  its  tisues.     More  than  one  hundred  fungi  have  been  enu- 
merated as  growing  upon  the  various  parts  of  the  tree,  including  the 
flowers  and  fruit,  a  great  majority  of  which  are  parasitic.     The  dis- 
eases  which  they  cause  may  be  best  discussed  under  the  following 
heads : 

DISEASES    OF   ROOTS. 

Root-rot — This  is  a  serious  disease  in  which  the  roots  undergo  a 
kind  of  dry-rot  without  any  apparent  cause.  It  is  probably  due  to  the 
presence  of  a  fungus,  since  in  other  trees  with  a  similar  rotting  of  the 
roots  the  trouble  has  been  traced  to  some  of  the  larger  fungi.* 

*See  H.  M.  Ward's  Timber  and  Some  of  Its  Diseases,  p.  142. 


THE    BOTANY    OF   THE    APPLE   TREE.  23 

DISEASES   OF   THE   TRUNK. 

Rotten  Heart. — This  is  probably  closely  related  to  the  root-rot. 
The  heart  wood  becomes  brittle  and  punky,  and  may  be  easily  snap- 
ped off  with  a  little  force.  The  threads  of  some  of  the  larger  fungi 
are  found  ramifying  through  the  woody  tissues.  It  may  be  that 
several  fungi  (pore-fungi,  and  toadstools)  are  concerned  in  this  dis- 
ease. Certain  it  is  that  a  small  ear-shaped  toadstool  (Schizophyllum 
commune)  always  appears  on  the  trunk  about  the  time  that  the  disease 
is  well  under  way.  Another  umbrella-shaped  toadstool  (Agaricus 
melleus)  is  known  to  be  concerned  in  the  heart-rot  of  various  timber 
trees,*  and  it  is  thought  by  many  botanists  to  be  the  chief  cause  of  the 
present  trouble. 

It  is  probable  that  the  fungi  of  Rotten  Heart  enter  through  wounds 
from  careless  and  injurious  pruning.  It  is  possible  that  they  may 
enter  through  the  wounds  made  by  grafting.  These  points  demand 
careful  inquiry. 

Black  Heart. — The  cause  of  this  common  disease  is  obscure.  It 
may  be  due  to  too  low  a  winter  temperature,  and  again  it  may  be  the 
effect  of  the  earliest  invasion  of  fungal  filaments.  Possibly  it  is  the 
result  of  some  of  the  other  general  causes  discussed  above.  It  de- 
mands further  study. 

Sun  Scald. — While  not  due  to  parasitism,  this  is  entered  here  in 
order  to  refer  the  reader  to  the  discussion  above  under  "  Unfavorable 
Atmospheric  Conditions." 

Blight. — Twig-blight  sometimes  extends  down  upon  the  trunk  of 
the  tree. 

See  the  following  discussion  of  blight  on  twigs  and  branches: 

DISEASES   OF   THE    BRANCHES   AND   TWIGS. 

Blight. — The  following  account  of  the  blight  of  the  apple  tree  is 
supplied  by  Mr.  A.  F.  Woods,  until  recently  assistant  in  the  botanical 
department  of  the  State  University,  now  assistant  pathologist  in  the 
Department  of  Agriculture,  Washington,  D.  C.: 

THE  "TWIG  BLIGHT"  OR  "FIRE  BLIGHT"  OF  THE  APPLE. 

This  disease  is  best  characterized  by  the  dying  of  the  twigs  from 
the  end  down.  In  severe  cases  the  smaller  limbs  are  often  attacked, 

*  H.  M.  Ward's  Timber  and  Some  of  Its  Diseases,  p.  155. 


24  NEBRASKA    STATE    HORTICULTURAL   SOCIETY. 

and  sometimes  the  larger  limbs,  and  even  the  trunk  of  the  tree  is 
killed.  The  same  disease  attacks  the  pear,  and  is  known  as  the  "pear 
blight.7'  It  is  much  more  severe  and  destructive  on  the  pear  than  on 
the  apple.  It  has  a  wide  distribution  in  North  America  and  is  the 
cause  of  great  loss  to  apple  and  pear  growers. 

Cause.  —  The  disease  is  caused  by  a  certain  minute  single-celled 
plant,  one  of  the  bacteria  named  Micrococcus  amylovorus  by  Professor 
Burrill,  but  since  called  Bacillus  amylovorus  (B.)  De  Toni.  Professor 
Burrill*  first  discovered  that  this  bacterium  was  the  cause  of  twig- 
blight.  He  inoculated  healthy  branches  with  the  juices  of  diseased 
ones,  thus  being  able  to  produce  the  "blight."  Dr.  J.  C.  Arthur,  f  by 
a  series  of  very  carefully  conducted  experiments, 
proved  beyond  doubt  that  the  disease  is  caused  by 
this  particular  bacterium  and  by  no  other.  Ba- 
G^us  amyhvorus  (B.)  De  T.  is  very  small,  one  to 
^  >  o  cncD  <  o  one  and  one-fourth  thousandths  of  a  millimeter 

FIG.  5.-Bacteria  which  long>  b-V  half  as  broad-  Thev  are  Oval  aud  co]or' 
produce  blight,  mag-  less,  either  single  or  attached  in  twos  or  threes. 
nified  1,00  times. 


young  succulent  parts  of  twigs  or  into  the  flowers,  increase  in  num- 
bers and  destroy  the  young  growing  cells  of  the  twigs  or  flowers,  thus 
causing  their  death. 

Infectious.  —  The  disease  is  considered  to  be  extremely  infectious,  the 
bacteria  being  carried  in  the  form  of  dust  from  tree  to  tree  bv  the 
wind.  Mr.  M.  B.  Waite,  of  the  Division  of  Vegetable  Pathology  in 
the  United  States  Department  of  Agriculture,  has  pointed  out  the 
fact  that  insects  play  a  very  important  part  in  distributing  these  germs. 
He  doubts  if  any  other  very  important  means  of  distribution  exists. 

Species  of  trees  affected.  —  The  disease  is  most  troublesome  in  the 
pear,  apple,  and  quince,  but  affects  many  other  near  relatives  of  these. 
The  different  varieties  of  apples  are  affected  in  different  degrees. 

Conditions  —  It  is  generally  held  by  investigators  and  those  ac- 
quainted with  the  disease,  that  watery,  succulent  growth  offers  the  best 
conditions  for  the  development  of  the  disease. 

Remedy  —  Removal  and  destruction  by  fire  of  the  diseased  parts  is, 
so  far  as  yet  known,  the  best  remedy.  Anything  that  will  cause  hardy 

*Proc.  Amer.  Assoc.  Adv.  Sci.,  vol.  XXIX,  1880,  p.  583. 
fProc.  Amer.  Assoc.  Adv.  Sci.,  vol.  XXXIV,  1885,  p.  295. 


THE    BOTANY    OF    THE    APPLE   TREE.  25 

growth  instead  of  watery,  succulent  growth  aids  the  tree  in  resisting 
attack. 

During  the  month  of  October,  1892,  the  Botanical  Department  of 
the  Agricultural  Experiment  Station  of  Nebraska  sent  out  a  list  of 
questions  with  the  object  of  bringing  together  the  experience  of  our 
horticulturists  concerning  "twig-blight"  of  the  apple.  There  were 
one  hundred  and  three  sets  of  questions  sent  out  and  fifty  sets  were  re- 
turned with  most  of  the  questions  answered.  While  the  Department 
regrets  that  there  were  not  more  answers  received,  still  it  believes  the 
results  of  the  inquiry  to  be  of  practical  value  to  the  fruit  growers  of 
the  state  and  may  at  least  serve  as  a  foundation  for  a  more  complete 
record. 

Record  of  Answers  to  Questions  1  and  %. 

(1.)  What  varieties  of  apples  have  you  found  least  affected  by  this 
disease,  and  (2)  what  varieties  most  affected? 

v AH/TIP  Least        Not  badly       Most 

affected.        affected,     affected. 

1.  Allen's  Choice 200 

2.  Autumn  Strawberry 010 

3.  Autumn  Swaar 001 

4.  Baldwin  0               0               1 

5.  Ben  Davis 23               1               2 

6.  Brier's  Sweet  Crab 001 

7.  Bentley's  Sweet 100 

8.  Buffington's  Early 200 

9.  Carolina  Eed  June 112 

10.  Chenango  Strawberry 202 

11.  Cole's  Quince 2               1               0 

12.  Cooper's  Early  White 007 

13.  Day 100 

14.  Dunlap 100 

15.  Duchess  of  Oldenburg 19               2               0 

16.  Domine 0               0             13 

17.  Dyer 1               0               0 

18.  Early  Harvest 501 

19.  Early  Pennock 0               0                1 

20.  Fall  Wine  Sap 210 

21.  Fameuse  (Snow) 1               0             11 


26  NEBRASKA    STATE    HORTICULTURAL    SOCIETY. 

Least        Not  badly       Most 
affected.        affected,     affected. 

22.  Fulton 100 

23.  Gano 1  0  0 

24.  Golden  Russet 004 

25.  Grimes7  Golden  Pippin  1  1  3 

26.  Haas 700 

27.  Hollow  Core 1  0  0 

28.  Hubbardston's  Nonesuch 100 

29.  HyslopCrab 1  0  8 

30.  Huntsman  Favorite 001 

31.  Iowa  Blush 900 

32.  Jonathan 426 

33.  Lawver 002 

34.  Maiden's  Blush Ill 

35.  Mann 004 

36.  Minkler 1  0  1 

37.  Missouri  Pippin  (Nickajack) 1  8 

38.  Milam 1  0  0 

39.  Monarch 010 

40.  Mother 100 

41.  McAfee's  Nonesuch 002 

42.  Northwestern  Greening 2  0  0 

43.  Northern  Spy 300 

44.  Otoe  Red  Streak 200 

45.  Perry  Russet 802 

46.  Pewankee 105 

47.  Plumb's  Cider 200 

48.  Price's  Sweet 100 

49.  Pomme  Grise 100 

50.  Rawle's  Janet 13  4  2 

51.  Randel'sBest 100 

52.  Red  Astrachan 404 

53.  Roman  Stem 200 

54.  Rome  Beauty 212 

55.  Rambo 003 

56.  Salome 301 

57.  Sheriff 200 

58.  Small  Red  Romanite...  600 


THE  BOTANY  OF  THE  APPLE  TREE.  27 

M._  Least          Not  badly     Most 

affected.        affected,     afiected. 

59.  Smith's  Cider 1               0               1 

60.  Sops  of  Wine 300 

61.  Stark 008 

62.  Summer  Queen 001 

63.  Sweet  June 300 

64.  Sweet  Pearmain 100 

65.  Sweet  Pear  Apple 0.0               1 

66.  Trenton  Early 100 

67.  Talman's  Sweet 0               0             10 

68.  Tetofsky 003 

69.  Transcendent  Crab 0               0              13 

70.  Utter 600 

71.  Walbridge -. 14               1               0 

72.  Wealthy 14               1                2 

73.  Westfield  Seek  No  Further 2               0               0 

74.  Whitney  No.  20,  Crab 601 

75.  Wine  Sap 24               0               3 

76.  William's  Favorite 100 

77.  Willow  Twig 1               1             12 

78.  Wagner 001 

79.  White  Winter  Pearmain 003 

80.  Yellow  Transparent 005 

81.  Yellow  Bell 1               0               0 

Nearly  all  Russian  Varieties 015 

Nearly  all  Crabs 007 

Hybrids  001 

Taking  out  those  varieties  that  have  at  least  six  favorable  reports 
with  very  few  or  no  unfavorable  reports  we  have  in  the  order  of  free- 
dom from  disease : 

1.  Duchess  of  Oldenburg.  7.  Haas. 

2.  Wine  Sap.  8.  Rawle's  Janet. 

3.  Ben  Davis.  9.  Small  Red  Romanite. 

4.  Walbridge.  10.  Utter. 

5.  Wealthy.  11.  Perry  Russet. 

6.  Iowa  Blush.  12.  Whitney  No.  20. 


28  NEBRASKA   STATE   HORTICULTURAL   SOCIETY. 

For  those  most  affected  we  find  in  order  named : 

1.  Transcendent  Crab.  7.  Hyslop  Crab. 

2.  Domine.  8.  Cooper's  Early  White. 

3.  Talman's  Sweet.  9.  Missouri  Pippin. 

4.  Willow  Twig.  10.  Yellow  Transparent. 

5.  Fameuse  (Snow).  11.  Golden  Russet. 

6.  Stark.  12.  Pewaukee. 

Both  of  these  lists  might  be  greatly  enlarged  were  there  more  data 
at  hand.  It  is  evident  from  the  reports  thus  far  compiled  that  very 
few,  if  any,  of  the  eighty-one  varieties  named  are  entirely  free  from 
the  disease  under  all  conditions.  Again,  there  are  some  generally  re- 
ported as  "bad  blighters"  that  appear  in  the  list  as  "least  affected." 
These  facts  indicate  the  possibility  of  so  controlling  the  growth  of 
the  tree  that  it  may  successfully  resist  the  attack  of  the  blight  bacteria. 

THIRD  QUESTION. — What  do  you  do  to  check  the  twig  blight? 

Cut  and  Burn. 

In  answer  to  this  question  there  were  twenty-one  correspondents 
who  "cut  out  and  burned  the  blighted  parts,  thus  controlling  the  dis- 
ease with  fair  success."  There  were  three  who  also  "cut  out  and 
burned  the  bad  blighters."  There  were  three  who,  "  in  addition  to 
the  destruction  of  blighted  parts  and  blighters,  also  stopped  cultiva- 
tion and  seeded  to  clover."  Two  correspondents  said  "  cut  out  and 
burn  the  blighted  parts  when  the  trees  are  through  blighting." 

Spraying. 

There  were  three  correspondents  who  used  spraying  mixtures, 
two  "with  no  success,"  and  one  who  did  not  say  whether  successful 
or  not. 

Root  Pruning. 

Root  pruning  is  said  by  one  correspondent  to  have  been  "  success- 
ful in  checking  blight  in  Talman's  Sweet  in  the  orchard."  Another 
correspondent  "  root  pruned  in  the  nursery  row." 

Salt  and  Lime. 

One  correspondent  used  a  liberal  application  of  "salt  and  lime  to 
the  surface  of  the  soil."  Another  used  "  lime,  ashes,  and  manure." 


THE  BOTANY  OF  THE  APPLE  TREE.  29 

Nothing. 

Six  correspondents  did  nothing,  and  seven  gave  no  answers  to  this 
question. 

FOURTH  QUESTION. — Have  you  noticed  anything  in  regard  to  lo- 
cality, slope,  altitude,  protection,  soil,  etc.,  that  favors  or  checks  the 
disease? 

Conditions  Favorable  to  Blight. 

"Trees  in  rich  and  hot  moist  localities,"  reported  by  seven  corre- 
spondents as  "  blighting  the  most.'7  Two  correspondents  reported 
"  blight  worst  in  wet  seasons."  Six  correspondents  said  "  trees  pro- 
tected by  timber  belts  so  as  to  prevent  free  circulation  of  air  blighted 
most."  Three  reported  "southern  slopes  favorable  to  blight,"  and 
one  reported  "  severe  pruning  followed  by  the  disease." 

Conditions  Unfavorable  to  Blight. 

Five  correspondents  reported  "trees  on  high  rolling  ground"  as 
"  least  affected."  Five  correspondents  reported  "trees  on  northern 
slopes  not  so  badly  affected  as  those  on  southern  slopes."  The  three 
who  reported  against  southern  slopes  should  be  considered  here,  mak- 
ing eight  in  favor  of  northern  slopes  as  opposed  to  southern.  One 
correspondent  said  that  "  a  wind-break  on  the  south  of  the  orchard 
aids  in  reducing  the  blight." 

FIFTH  QUESTION. — Are  young  and  old  trees  affected  to  the  same 
degree  ? 

Twenty-two  correspondents  reported  "young  and  old  trees  affected 
to  about  the  same  degree."  Six  correspondents  reported  "young  trees 
most  affected."  Four  reported  "old  trees  most  affected."  Sixteen 
correspondents  gave  no  answers  to  this  question. 

SIXTH  QUESTION. — What  did  you  estimate  your  annual  loss  to  be 
by  this  disease? 

Seven  correspondents  reported  "loss  small  on  account  of  destruction 
of  diseased  parts."  Two  reported  "loss  small  on  account  of  planting 
non-blighters."  Eleven  correspondents  reported  an  average  loss  of 
"five  to  ten  per  cent."  More  than  ten  per  cent  (fifteen -to  fifty), 
mostly  in  the  nursery  row,  reported  by  five  correspondents.  "Loss 
small  with  no  care  taken,"  reported  by  two  correpondents.  Four  cor- 


30  NEBRASKA   STATE    HORTICULTURAL   SOCIETY. 

respondents  said  that  their  trees  were  "  not  troubled  with  blight,"  and 
sixteen  gave  no  answer  to  this  question. 

Summary. 

In  bringing  together  the  results  of  this  inquiry  in  the  form  of  a 
summary,  I  shall  simply  indicate,  with  few  comments,  the  direction 
of  the  evidence  gathered  above.  «ISS' 

Varieties  Affected. 

The  evidence  indicates  that  certain  varieties  of  apple  trees  are  less 
affected  than  others,  but  that  few  if  any  varieties  are  proof  against  the 

disease. 

Conditions. 

It  appears  that  such  conditions  as  hot,  moist  locality,  rich  soil,  lack 
of  free  circulation  of  air  (on  account  of  protection  by  wind-breaks, 
etc.),  cause  a  watery  or  succulent  growth  of  the  tree  which  is  favorable 
to  blight. 

On  the  other  hand,  high  rolling,  well  drained  ground  of  north 
slope  and  free  circulation  of  air  offers  the  most  favorable  conditions 
for  hardy  growth  of  the  trees,  which  are  therefore  less  liable  to  blight. 

How  to  Check  the  Disease. 

So  far  as  yet  known  the  best  way  to  check  the  disease  is  to  cut  off 
the  blighted  twigs  several  inches  below  where  they  are  dead  and  burn 
them  immediately. 

Root  pruning  may  cause  a  decrease  in  the  water  supply  and  thus 
be  valuable  in  checking  the  succulent  growth,  but  in  many  cases,  es- 
pecially in  nursery  stock,  this  is  objectionable,  because  it  is  too  great 
a  check  to  growth. 

Stopping  cultivation  and  seeding  to  clover  may  check  too  rapid 
growth.  The  effect  on  the  tree  of  salt,  lime,  and  ashes  applied  to  the 
surface  of  the  ground  needs  further  investigation. 

Spraying  has  thus  far  proved  to  be  of  no  value  in  checking  the 
"Fire  Blight"  in  diseased  trees  or  in  protecting  them  from  attack. 

Finally,  if  you  are  going  to  plant  an  orchard  and  wish  to  guard 
against  "  blight/7  the  indications  are,  for  Nebraska:  First,  plant  va- 
rieties lea^st  liable  to  blight;  second,  plant  on  high,  rolling,  well  drained 
ground  of  northerly  slope;  and  last,  plant  no  wind-breaks,  except  pos- 
sibly on  the  south  or  southwest,  at  some  distance  from  the  orchard. 


THE  BOTANY  OF  THE  APPLE  TREE. 


31 


Black  Heart. — Both  branches  and  twigs  are  subject  to  this  disease, 
which  is  discussed  under  the  "Diseases  of  the  Trunk.'7 


DISEASES   OF   THE   LEAVES. 

Powdery  Mildew. — The  leaves  of  young  trees,  especially  those  in  the 
nursery,  are  quite  subject  to  the  attacks  of  a  powdery  mildew  which 
covers  their  surface  with  a  white  powdery  coat.  The  leaves  soon  be- 
come somewhat  curled  and  wrinkled,  and  eventually  are  greatly  in- 
jured. The  fungus  which  causes  this  disease  is  one  of  the  Simple 
Sac-Fungi  (Perisporiacece)  and  bears  the  scientific  name  of  Podos- 
phcera  oxycanthce.  It  consists  of  slender,  white,  branching  threads 
which  creep  over  the  skin  of  the  leaf,  sending  in  little  suckers  here  and 
there,  which  take  food  matter  from  the  cells.  At  length  many 
branches  are  sent  up  at  right  angles  to  the  surface  (Fig.  6,  A).  These 


wr 


FIG.  6. — The  Powdery  Mildew.  A,  fragment  of  a  thread 
with^a  vertical  branch  producing  summer  spores;  B, 
spore-sac  from  the  fruit;  C,  one  of  the  ripe  fruits  with 
its  radiating  appendages.  All  much  enlarged. 

quickly  break  up  into  summer  spores,  and  as  these  form  in  great  num- 
bers they  give  the  leaves  the  well-known  white-powdery  appearance. 
The  summer  spores  blow  away  in  the  wind  and  under  favorable  con- 
ditions germinate  quickly  and  give  rise  to  a  new  growth  of  the  fungus. 
Later  in  the  season,  usually  not  until  the  autumn,  the  fungus  produces 
its  small  spherical  fruits  (Fig.  6,  C),  which  are  black  in  color  and 
barely  large  enough  to  be  seen  with  the  naked  eye. 


32  NEBRASKA   STATE    HORTICULTURAL   SOCIETY. 

ID  the  interior  of  each  fruit  there  is  at  maturity  a  single  spore-sac 
(Fig.  6,  B)  containing  eight  roundish  spores.  The  thick  wall  of  the 
fruit,  and  the  thickish  wall  of  the  spore-sac,  form  a  sufficient  protec- 
tion to  the  spores,  which  are  thus  enabled  to  pass  the  winter  un- 
harmed. The  next  spring  they  germinate  in  the  masses  of  decaying 
leaves,  and  thus  easily  infect  the  lower  leaves  of  seedling  trees,  from 
which  they  readily  pass  to  older  trees. 

Burning  the  leaves  in  the  fall  or  early  winter  will  reduce  the  lia- 
bility to  the  propagation  of  the  disease  next  year. 

Spraying  the  trees  several  times  in  the  early  part  of  the  year,  as 
soon  as  the  disease  appears,  with  a  watery  solution  of  the  arnmoniacal 
carbonate  of  copper*  will  kill  the  fungus. 

Scab. — The  disease  of  the  leaves  here  referred  to  is  known  also  as 
"leaf  blight,"  a  term  of  doubtful  propriety,  as  it  is  liable  to  lead  to 
confusion  with  the  true  blight  (see  below).  It  is  produced  by  the 
same  minute  fungus  which  is  the  cause  of  the  scab  on  the  fruit;  in 
fact  we  have  here  a  case  of  the  same  disease  attacking  both  leaves  and 
fruit.  The  leaves  affected  by  scab  become  yellowish,  and  on  the  un- 
der surface  show  a  more  or  less  abundant  growth  of  blackish,  jointed, 
branching  threads  (Fig.  7).  Spraying  with  ammoniacal  carbonate  of 
copper  is  recommended  for  this  form  of  the  scab. 

Rust. — This  disease  is  abundant  in  some  parts  of  the  east,  but  so 
far  as  I  am  aware  it  has  not  yet  appeared  in  Nebraska.  It  will 
doubtless  reach  our  orchards  in  time,  and  so  may  properly  be  noticed 
here.  It  consists  of  bright  yellow  patches  upon  slightly  thickened 
portions  of  the  leaf  surface.  On  close  examination  with  a  hand  lens 
these  patches  are  seen  to  consist  of  yellow  cup-shaped  fruits  of  a  fun- 
gus which  grows  in  the  interior  of  the  leaf,  finally  rupturing  the  skin 
to  bring  the  spores  to  the  surface.  The  spores  germinate,  not  on  ap- 
ple leaves  as  might  be  supposed,  but  upon  the  red  cedar,  producing 
the  kind  of  rust  on  it  known  as  "  cedar  apples,"  and  the  spores  from 
the  latter  infect  the  apple  leaves  again. 

When  abundant  it  is  a  most  serious  disease.  It  is  noticed  here  in 
order  to  forewarn  our  orchardists.  On  its  first  appearance  the  trees 

*  Ammoniacal  carbonate  of  copper  is  prepared  as  follows: 

Carbonate  of  copper 5  ounces. 

Ammonia  (liquid) 3  pints. 

Mix  thoroughly  until  the  copper  is  dissolved. 

Add  water 45  gallons. 


THE  BOTANY  OF  THE  APPLE  TREE.  3£ 

must  be  sprayed  with  the  ammoniacal  carbonate  of  copper  solution, 
and  it  may  be  advisable  to  watch  the  red  cedar  trees,  also,  pretty 
closely  in  the  spring  of  the  year  for  cedar  apples.  Spraying  these 
trees,  also,  might  be  useful. 

Brown  Spot. — In  some  of  the  eastern  states  the  leaves  of  apple 
trees  are  sometimes  destroyed  by  a  minute  fungus  (Phyllosticta  pirina). 
While  I  have  not  myself  seen  the  work  of  this  parasite  in  Nebraska, 
specimens  were  collected  at  Lincoln  three  or  four  years  ago  by  Mr. 
H.  J.  Webber,  then  assistant  in  the  Botanical  Laboratory  of  the  State 
University,  who  makes  the  following  record  regarding  it :  "  On  ap- 
ple leaves.  Abundant  and  frequently  destructive.  November  12. 
Lincoln."*  It  is  therefore  certain  that  it  is  in  the  state,  and  it  is  prob- 
ably only  a  question  of  time  when  our  orchards  will  be  seriously 
troubled  by  it. 

Professor  Alwood  of  Virginia  describes  it  as  follows :  f 

"  The  external  appearances  are,  in  the  early  stage,  more  or  less  nu- 
merous quite  minute  spots  on  the  leaves,  circular  in  outline,  and  of  a 
brick-red  color.  These  grow  rapidly  larger,  maintaining  a  nearly  cir- 
cular form,  and  show  at  the  center  a  pale,  circular  spot  of  straw-like 
color.  Occasionally  several  spots  coalesce  and  show  a  large  area  of 
diseased  tissue.  The  first  attack  occurs  here  [in  Virginia]  shortly 
after  blooming,  about  the  first  of  May,  and  by  June  20,  the  foliage 
first  attacked  is  falling.  About  this  later  period  the  foliage  becomes 
very  seriously  spotted  from  a  second  attack,  and  a  third  outbreak  oc- 
curs about  the  last  of  July.  Thus  this  disease  develops  three  succes- 
sive outbreaks  in  the  course  of  the  summer,  and  unless  promptly 
treated  in  its  early  stages,  promises  to  be  the  most  serious  disease  of 
the  foliage  orchardists  have  had  to  contend  with." 

It  is  suggested  that  the  careful  burning  of  the  leaves  which  fall 
from  the  trees  may  be  useful  in  checking  the  rapid  spread  of  this 
disease.  Spraying  the  foliage  with  Bordeaux  preparation  J  at  the 
time  the  tree  is  in  bloom  is  recommended  also. 

*  Appendix  to  the  Catalogue  of  the  Flora  of  Nebraska,  Second  Edition,  p.  16. 
t  Bulletin  No.  17  of  the  Virginia  Agricultural  Experiment  Station,  1892,  p.  62. 
JThe  Bordeaux  preparation  is  made  as  follows  for  this  use: 

Sulphate  of  copper , 4  pounds. 

Fresh  lime 5  pounds. 

Water 50  gallons. 

Dissolve  the  copper  and  the  lime  separately  and  then  mix  the  solutions.  This  is 
what  is  known  as  a  weak  solution;  it  is  usually  made  two  or  three  times  as  strong. 


34  NEBRASKA    STATE    HORTICULTURAL   SOCIETY. 

Blight. — When  the  twigs  are  blighted  the  leaves  die,  hence  it  is  com- 
monly said  that  the  leaves  are  blighted,  although  usually  the  trouble 
is  in  the  twigs.  See  the  discussion  of  Blight  by  Mr.  Woods  under 
41  Diseases  of  Branches  and  Twigs,"  on  preceding  pages  of  this  paper. 

DISEASES   OF   THE   FLOWERS. 

Blight. — It  frequently  happens  that  the  flowers  of  the  apple  sud- 
denly wither  and  turn  brown  with  no  apparent  cause,  no  insects  what- 
ever being  present.  An  examination  of  a  good  many  specimens  from 
orchards  within  the  state,  as  well  as  from  without,  shows  that  we 
have  here  a  case  of  genuine  blight  produced  by  bacteria  identical 
with  those  in  the  twigs.  See  the  discussion  of  Blight  by  Mr.  Woods 
under  "Diseases  of  Branches  and  Twigs,"  on  preceding  pages  of  this 
paper. 

DISEASES   OF    THE   FRUIT. 

Scab. — But  few  apples  are  entirely  free  from  this  disease.  In  its 
mildest  form  it  produces  little  black  specks  on  the  skin,  which  do  lit- 
tle or  no  harm,  but  when  more  virulent  it  forms  large  black  patches 
and  produces  much  distortion.  The  fungus  which  causes  scab  is 
composed  of  dark-colored,  jointed,  branching  threads  which  creep  over 
the  surface,  invading  the  superficial  cells  (Fig.  7).  After  the  growth 
has  continued  for  some  time,  if  the  conditions  have  been  favorable, 
the  fungus  forms  denser  black  patches  in  which  it  produces  great 
numbers  of  spores  (Fig.  8).  The  particular  manner  of  growth  of 
these  spores  is  shown  in  Fig.  8,  at  B,  and  a  few  of  the  detached  spores 
are  shown  at  S.  When  this  fungus  makes  good  progress  in  its  growth 
while  the  apple  is  still  small  it  produces  great  distortion,  but  if  its 
•development  is  later  the  apple  is  but  little  changed  in  shape,  as  in 
Pig.  8. 

The  fungus  is  one  of  the  so-called  "  Imperfect  Fungi,"  and  is 
known  in  science  by  the  name  of  Fusidadium  dendriticum.  As  stated 
above  (under  "Diseases  of  the  Leaves")  it  is  the  same  one  which  at- 
tacks the  leaves.  It  lives  perennially  upon  the  bark  of  the  twigs,  and 
from  these  it  easily  passes  to  the  leaves  and  young  fruit.  Infection 
takes  place  also  through  the  growth  of  the  spores,  hence  the  burning  of 
the  leaves  in  the  fall  would  be  useful. 

Professor  Alwood,  of  Virginia,  recommends  spraying  the  trees  in 


THE  BOTANY  OF  THE  APPLE  TREE. 


35 


early  spring  before  the  opening  of  the  buds  with  a  solution  of  lye,* 
which  he  says  he  "has  clearly  demonstrated  very  materially  checks 
the  outbreak  of  scab." 


FIG.  7. — Apple  scab.  A,  a  mag- 
nified view  of  a  cl  uster  of  small 
specks;  B,  portion  of  the  fun- 
gus highly  magnified;  C,  part 
of  B  magnified  still  more. 


FIG.  8. — Apple  scab.  A,  an  apple 
with  well  developed  scab;  B, 
section  through  a  scab  highly 
magnified,  showing  a  few  de- 
tached spores  at  S. 


Bitter-rot  or  Ripe-rot. — This  troublesome  disease  appears  upon  the 
surface  of  the  mature  apple  in  the  form  of  brownish  or  blackish  spots 
which  are  at  length  studded  with  minute  black  points  (Fig.  9). 
These  diseased  spots  extend  deep  into  the  fruit,  and  are  noted  for  hav- 
ing a  peculiarly  bitter  taste.  The  fungus  which  produces  bitter-rot 
is  also  one  of  the  so-called  "Imperfect  Fungi,"  and  is  known  as 
Gloeosporium  frutigenum. 

*The  solution  used  by  Professor  Alwood  is  made  as  follows: 

Concentrated  lye 8  cans. 

Water 50  gallons. 

|  In  Bulletin  17  of  Virginia  Agricultural  Experiment  Station,  p.  64. 


36 


NEBRASKA   STATE   HORTICULTURAL   SOCIETY. 


Professor  Bailey  recommends  spraying  the  trees  early  in  August 
with  ammoniacal  carbonate  of  copper.*  Professor  Alwood  also  rec- 
ommends this,  and  further  advises  allowing  hogs  to  eat  up  all  affected 
apples,  thus  destroying  the  fungus,  f 


FIG.  9. — An  apple  affected  with  bitter- rot. 


FIG.  10. — A,  a  magnified  section  through  one  of  the 
dark  points  in  Fig.  9,  showing  spore-bearing  threads; 
B,  more  highly  magnified  spores;  C,  spores  germi- 
nating. 

*  In  Horticulturist's  Rule  Book,  p.  45. 

f  In  Bulletin  No.  17  of  the  Virginia  Agricultural  Experiment  Station,  p.  62. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN     INITIAL     FINE     OF     25     CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


15  J932 
WOV    16   1932 


DEC    151938 


LD  21-50m-8,-32 


678005 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


